Lubricant compositions



United States Patent 3,223,628 LUBRICANT COOSITIONS Donald E. Loefller, Walnut Greek, Calih, assignor to Shell Uil Company, New York, N.Y., a corporation of Delaware No Drawing. Filed Apr. 11, 1963, Ser. No. 272,226 7 Claims. (Cl. 25228) This invention relates to lubricating grease compositions useful at very high temperatures. More particularly, it relates to clay-thickened greases which are capable of use in high-temperature applications, and which are, at the same time, resistant to disintegration in the presence of water.

The manufacture of greases gelled with inorganic colloids and particularly with clay has been disclosed in the prior art. In order to maintain the water stability of such greases, it is necessary to provide the clay with hydrophobic surfaces or otherwise to protect it. Various means for achieving this have been proposed in the art such as providing hydrophobic surface-active agents including amines, imidazolines, amidoamines and the like. Even though the structure of such greases is stable at extremely high temperatures, most conventional surfactantcontaining clay-thickened greases are inadequate for use at high temperatures because of the thermal and/ or oxidation instability of the surfactant itself. This special high-temperature problem has been solved to some extent by the waterproofing of such greases with thermally stable thermosetting resins, instead of relatively unstable cationic surfactants. However, lubricating compositions suitable for general use throughout the mechanical arts should possess good lubricating properties when operated in either a dry or Wet environment. This latter condition is particularly prevalent in such industrial uses as steel rolling mill applications and the like. Furthermore, the yield of greases prepared from such gelling agents must be as high as possible. The use of resin-coated gelling agents per se has by no means been a panacea for these latter two problems.

It is therefore an object of this invention to provide new clay-thickened grease compositions suitable for use at extremely high temperatures, which are resistant to the leaching action of water and which can be produced with only a small amount of clay gelling agent.

Now, in accordance with the present invention, it has been found that greases exhibiting high water resistance and excellent thermal stability at extremely high temperature, both at high yield comprise a lubricating oil gelled to a grease consistency with a colloidally dispersed clay, bearing on its surfaces a resin formed from the co-condensation reaction of melamine and benzoguanamine with an aliphatic aldehyde, the polymer-to-clay weight ratio being from 0.8 to 5. Preferably the compositions comprise an organosilicone fluid of lubricating oil viscosity gelled to a grease consistency with a colloidally dispersed clay, the surfaces of the clay bearing the abovementioned proportions of melamine-benzoguanamine-aldehyde resin.

The colloidal gelling or thickening agents to be employed are especially selected for use in high-temperature grease compositions due to their relatively inert character at these high operating temperatures. While clays of low base exchange capacity, such as Georgia clay, Attapulgite and the like, may be utilized, it is preferred that a high base exchange clay, such as Wyoming bentonite or hectorite, be employed.

While the present invention is especially directed to extreme high-temperature lubricating greases, such greases may be employed for normal operating conditions as well. Likewise, superior greases for less severe applications can also be made in accordance with the invention by selection of the lubricating oil base stock. In this regard, most mineral oils are stable up to about 300 F., while synthetic esters are useful at temperatures up to about 350'- 400 F. In this latter category are synthetic lubricating oils of known types, such as the phosphorus esters, silicon esters and aliphatic esters formed by esterification of aliphatic dicarboxylic acids with monohydric alcohols. Typical species of these materials include tricresyl phosphate, dioctyl phthalate, bis(2-ethylhexyl)sebacate and the like.

Lubricants to be employed at temperatures in excess of about 400 F. are those having an inherent high thermal stability including the halocarbons and organo-silicone fluids. The halocarbons may be those described in Peterson et al. patent, US. 2,679,479, and include especially the fluorocarbon oils, preferably distilling above about 200 C. at atmospheric pressure. The most useful class of lubricants for grease compositions to be utilized at temperatures in excess of about 400 F. include the organosubstituted silicone fluids of lubricating oil viscosity. Of primary interest for this invention are the unreactive, thermally stable silicone fluids, which will generally be of the following types:

Methyl silicone fluids The above types of silicone fluids, in addition to being the most thermally stable are also the most readily available in commercial quantities. Methyl phenyl fluids are particularly preferred because of their still greater thermal stability.

It will, of course, be recognized, that other organic groups as well as inorganic groups can replace a portion of the methyl groups, e.g., hydrogen, lower alkyls, halogens, etc. They are, however, generally too reactive and/or thermally unstable for high-temperature applications, though from the standpoint of mere grease formation and use at temperatures at which they are stable, they are quite satisfactory for the grease compositions of the invention.

The viscosity of such polymer or copolymer is, of course, dependent upon the reaction conditions employed in preparing the same, e.g., the polymers of dimethyl silicone vary from thin liquid to viscous liquid to solid resins, depending upon the conditions under which they are prepared. It is the liquid polymers and copolymers having a preferred viscosity exceeding 500 Saybolt seconds at F., which are usually employed in preparing the new compositions.

The thermosetting resins contemplated for use in the compositions of this invention are complex resins, the structure of which is not known, formed by the condensation reaction of melamine and benzoguanamine together with various aldehydes. These amine resins do, however, fall within the class known as aminoplasts as described in the book entitled Fundamentals of Plastics, edited by Richardson and Wilson, Chapters and 6.

The aldehydes which may be polymerized with the amino compounds include either saturated or unsaturated aldehydes, which may, in turn, be either aliphatic or cyclic. Among those which may be used are formaldehyde, acrolein, furfural, acetaldehyde and crotonaldehyde. For reasons of reactivity as well as thermal stability, it is preferred to use aldehydes containing no more than about six carbon atoms. In the case of aliphatic aldehydes, it is particularly preferred to use only lower alkyl aldehydes, viz. those containing from 1 to 4 carbon atoms per molecule.

In order for the resultant grease composition to have satisfactory lubricating properties upon prolonged exposure to evaporation and oxidation, it is imperative that the weight ratio of the resin to the clay be confined to quite narrow limits. Specifically, it has been found that if the resin-to-clay ratio is less than 0.8, the grease may become too fluid upon prolonged exposure to high-temperature operating conditions. A resin-to-clay weight ratio of between 1.0 and 1.5 is especially preferred. Though larger amounts of resin, up to five times the clay weight, may be used, the effectiveness of such heavily coated clay to form a stable grease structure is reduced thereby.

Likewise it has been found that the ratio of the aldehyde to the melamine and benzoguanamine exerts a profound eifect on the ability of the grease to maintain good lubricating consistency, and that the aldehyde-to-amine ratio must be maintained between quite narrow limits. More particularly, it has been found that satisfactory plasticity of the grease at high temperatures is maintained only if the aldehyde to amine equivalent ratio is maintained between 0.9 and 1.5. At a ratio of 0.9 or less, the grease becomes too dry to lubricate well, and at 1.5 or more the grease becomes crumbly. An aldehyde-to-amine equivalent ratio of 1.0 to 1.4 is therefore preferred. Equivalent ratio as used herein refers to the ratio of reactive valences contained in thefractional groups of the two materials being compared. Thus, the equivalent ratio of one mole of aldehyde to one mole of melamine is 2:6 or 0.3, and to one mole of benzoguanamine is 2:4 or 0.5.

In addition to these important relationships of the resin to the clay and the aldehyde to the amine, it has also been found that the ratio of the two amine reactants exerts significant effects on both the water resistance and the yield of the grease composition, which effects are quite unexpected in view of the inability of the corresponding single amine-containing resins to impart these same properties. For this reason, the molar weight ratio of melamine-to-benzoguanamine in the resin with which the clay is coated must be within the limits of from 0.8:1 to 5:1, and preferably from 1:1 to 4:1.

Little has been said herein about the process for preparing the greases of the invention since many such procedures are well known in the art. However, all have in common the preparation of an aqueous suspension of the clay prior to forming the resin thereon. Depending upon the physical properties of the particular clay used, the suspension may be a slow-settling slurry or it may be in the form of a more stable hydrogel. Though within this context, the form of the dispersion is not an essential aspect of the invention, the preferred clays happen to form a hydrogel upon being dispersed in water. It is, however, a necessary limitation to the compositions of the invention that they be prepared from an aqueous y i p which. h been aci i ed wit a t g mineral acid.

Normally, in order to keep the clay hydrogel in workable (fluid) cencentration, it is preferred that the clay be dispersed to yield a hydrogel containing between about 0.25% and about 3% by weight of dry clay, based on the hydrogel before mechanical separation of water therefrom. This percentage is based upon dry weight of de-gangued clay and not upon the dry weight of clay containing naturally occurring contaminants. While the clay is largely dispersed throughout the entire body of the water in which it is incorporated, it is in the form of jelly-like colloidal globules which can be isolated by mechanical separation from a large part of the water to yield a clay hydrogel of substantially increased clay content without shrinking the expanded colloidal structure of the clay. By mechanical separation is meant any process for the separation of water from the colloid which does not involve a change in physical state such as occurs in normal evaporation methods and the like. Consequently, mechanical separation normally includes filtration techniques and accel erated substitutes therefor, such as centrifuging. This mechanical separation is performed subsequent to the addition to the clay hydrogel of the above-described aminoplast-forming amino compounds. The mechanical separation can take place at any desired temperature, room temperature being that preferably employed, although any temperature up to that of the boiling point of water may be utilized.

It is essential in the process that the amines and aldehyde be reacted in the presence of a minor amount of a strong mineral acid in the hydrogel. Moreover, the acid must be added in an amount in excess of that required to acidify the surfaces of the clay particles dispersed throughout the hydrogel. The amount of acid to acidify the clay, i.e., to replace all the basic metals (mostly sodium, potassium, calcium) contained on the clay, will vary depending upon the acid which is used and the base exchange capacity of the clay. However, in the case of hectorite clay to be acidfied with phosphoric acid, the amount of acid must be at least over 7% and preferably about 20% by weight, basis dry clay weight. On the other hand, no more than about 50% and preferably no more than 35% by weight acid should be used. Though phosphoric acid is the preferred strong mineral acid, other mineral acids such as hydrochloric and sulfuric acid may be employed.

The examples which follow will illustrate the unexpectedly superior properties of applicants grease compositions and the important limits so necessary in attaining these superior properties.

EXAMPLE I A resin-coated clay-thickened grease in accordance with the invention was prepared as follows:

To an aqueous slurry of the degangued hectorite clay containing 1.73% by weight clay was added an amount of 8.5% solution of H PO equivalent to 0.14 part by weight H PO per part of clay. Melamine was then added to the acidified clay slurry and thoroughly mixed therewith, after which benzoguanamine was added in the same manner. Formaldehyde (37% solution) in an amount equivalent to 064 part by weight per part of total amine was admixed with the amine-containing slurry, after which the mixture was boiled gently for 15 minutes. The boiled mixture was filtered, the residue was Washed with hot water and the residue was refiltered. To the washed and filtered residue was added a phenylmethy'lsiloxrane oil (DC 550) and an 18% solution of sodium sebacate corrosion inhibitor. The mixed oil and residue were heated at 275 F. to effect dehydration and the dehydrated mixture was milled two times. The resultant grease had an unworked penetration of 235. Because of relative hardness of the grease, 17% by weight more oil was added to the grease, which was milled once again. The resultant grease had an unworked penetration of 260 and its clay content was 7.3% by weight, exclusive of the resin thereon. The

resin-to-polymer ratio was 1.1. The proportions of the ingredients of the above were as follows:

The use of aminoplast thermosetting resins for hightemperature clay greases is, of course, well known. However, such greases are not uniformly satisfactory in their water resistance or yield. This lack of universally satisfactory properties as well as the quite unexpected superiority of the grease composition of the invention is illustrated by the following example.

EXAMPLE II Three separate greases were prepared by the process used in Example I, using a diiferent resin in each case. A melamine-formaldehyde resin was formed in Sample A, a benzoguana-mine-formaldehyde was formed in Sample B, and a benzoguanamine-melamine-formaldehyde resin containing an equimolar mixture of the two amines was used in the third sample. Each of three greases, which met the requirements for an N.L.G.I. No. 2 grade grease, was subjected to ASTM test procedure D 126'4-53T to determine the water washout characteristics of the three greases.

In the water-washout test the grease is packed in a ball hearing which is inserted in a housing with specified clearances and rotated at about 600 r. p.m. Water at the specified test temperature (here 175 F.) impinges on the Thus it can be seen that while the benzoguanamine resin produced a good yield, the resultant grease had extremely poor water resistance. Conversely, the melamine resin gave a relatively poor yield but excellent water resistance. The resin produced from an equimolar mixture of the two amines, however, had both excellent water-resistance and yield. The yield from the mixed amine resin was in fact better than that obtained from either of the resins produced from the single amines.

At this point, it is well to mention that the mixed amineformaldehyde resin is not a mere mixture of the resin formed from the condensation of benzoguanamine with the aldehyde and of melamine with the aldehyde. To the contrary, it is a much more complex resin since it is formed by the interaction of all three constituents. Because of the complexity of the reaction and the resulting resin structure, which is not fully understood, there is little, if any, predictability of the extrinsic effects of such resins. This lack of predictability is illustrated also by the many critical limitations upon resin composition, as regards the relative proportions of its three constituents, and upon the relative proportions of resin and polymer, all of which were discussed hereinabove. The necessity for these various limitations is illustrated by the following example:

EXAMPLE III A large number of No. 2 grade greases were prepared in the same manner as Example I in order to examine the effect of compositional variables. Each of the resultant greases was subjected to the ASTM Water Washout test (D 1264-5 3T) and to a high-temperature evaporation and oxidation test.

The high-temperature test comprised heating a thinfilm sample of the grease on a smooth fiat plate in the presence of air for 300 hours at 450 F., after which the Weight loss of the sample was measured and the texture of the grease was observed. The results of these tests were as follows:

Table II [Phenyl methylpolysiloxane oil (DC-710) used in each grease. 17% H POdbased on clay) used in preparation of slurry] Water High Temperature Aldehyde Clay to Washout Stability Test, 300 Resin- Amine to-Amine Yield N0. Test at hours at 450 F. to-Clay Sample No. Amine Ratio Ratio 2 Grade 175 F. Ratio (molar) (equiv (Percent (Percent (\vt.)

wt.) wt. loss) (Percent (Texture) wt. loss) 1 Melamine 1.1 7. 2 1.0 0. 9 6. 8 1. 2 1.1 5. 5 1. 2 1. 3 6. 4 1. 2 1. 1 6. 1 1. 4 1. 5 5.8 1. 4 1. 2 ca. 12 1.0 1. l 8. 7 1. 2 1. 2 10. 0 1. 2 1. 1 5. 5 1. 2 1. 1 7. 1 1. 1 1. 1 6. 3 1. 2

1 Formaldehyde (37% solution).

bearing housing at a rate of 5 ml. per second. The weight amount of grease washed out in one hour is then measured to determine the resistance of the grease to water washing.

The results were as follows:

From samples 1 and 7 it is evident from the poor yield that about 0.8 is the lower limit for the weight ratio of resin to clay. Comparison of samples 2, 5 and 6 shows that the aldehyde-amine equivalent ratios of 0.9 or less will yield greases which become too dry and thus lose their lubricating properties at high temperatures and that at ratios of 1.5 and above, the greases will crumble and lose their lubricating properties because of change in structure. From samples 3, 4, S and 9, it can be seen that all greases having aldehyde-amine ratios between these limits and which had resin-clay ratios of 1.0 or above were quite satisfactory in the high-temperature stability test.

The test results of samples 10, 11 and 12 show quite graphically (1) the very great advantage of using the twoamine resin instead of either of the single-amine resins and (2) the profound and unexpected effect of the relative proportion of the amines in the two-amine resin systems. In all ratios of amines, the two-amine resin-containing greases exhibited yields comparable to the melamine resin-containing greases and clearly superior to the benzoguanamine resin-containing greases. Furthermore, it is evident from the water washout tests that within the limits of amine molar ratios (melamine-tobenzoguanamine) from about 0.8 to about 4.0, the Water resistance of the greases of the invention were as good as the 'benzoguanamine resin greases and many times superior to the melamine-containing greases. It is especially interesting to note that in increasing the ratio of melamine from 1:1 at least to 3:1, an increase in water resistance was observed.

The importance of treating the clay with an excess of acid over that which is required to acidify the surface of the clay is illustrated by the following example:

EXAMPLE IV Two greases, each having the same relative proportion of the two amines, formaldehyde and clay, were made in the same manner as in Example I except that clay slurry in one did not contain an excess of H PO over that required to acidify the surfaces of the clay particles. The washed and filtered residue of each was added to the lubricating base oil (DC-710 silicone oil) in an amount sufficient to yield a N.L.G.I. No. 2 Grade grease. The samples were each tested by means of the ASTM Water Washout test and the aforementioned stability test, the results of which were as follows:

Amine ratio: 1:1 molal basis, melamine-to-benzoguanamine Aldehyde-amine ratio: 1.1 :1 equivalent Polymer-clay ratio: 1.2: 1 by weight From the above data it is quite evident that formation of the resin in the presence of an excess of mineral acid is very advantageous from the standpoint of yield and vitally necessary from the standpoint of water resistance.

I claim as my invention: 1. A grease composition consisting essentially of a major amount of a lubricating base oil gelled to grease consistency with a colloidally dispersed clay, said clay bearing on the surfaces thereof from 0.8 to 5.0 parts by weight, basis clay, of a resin formed by the co-condensation reaction of the amines melamine and benzoguanamine with an aliphatic aldehyde having up to about 6 carbon atoms, said resin having been formed in the presence of a mineral acid in excess of that required to acidify the surfaces of the clay, the molar ratio of melamine-to-benzoguanamine being from 0.811 to 5 .0: 1, and the equivalent ratio of aldehyde to aliphatic amines being between 09:1 and 1.5:1.

2. A grease composition consisting essentially of a major amount of a lubricating base oil gelled to grease consistency with a colloidally dispersed clay, said clay bearing on the surfaces thereof from 1.0 to 5.0 parts by weight, basic clay, of a resin formed by the co-condensation reaction of the amine-melamine and benzoguanamine with an aliphatic aldehyde having up to about 6 carbon atoms, said resin having been formed in the presence of a mineral acid in excess of that required to acidify the surfaces of the clay, the molar ratio of melamine-tobenzoguanamine being from 0.8:1 to 5.0: 1, and the equivalent ratio of aldehyde to aliphatic amines being between 0.921 and 1.5:1.

3. A grease composition consisting essentially of a major amount of a lubricating base oil gelled to grease consistency with a colloidally dispersed clay, said clay bearing on the surfaces thereof from 1.0 to 5.0 parts by weight, basis clay, of a resin formed by the co-condensation reaction of the amines melamine and benzoguanamine with an aliphatic aldehyde having up to about 6 carbon atoms, said resin having been formed in the presence of a mineral acid in excess of that required to acidify the surfaces of the clay, the molar ratio of melamine-to-benzoguanamine being from 1.0:1 to 4.021, and the equivalent ratio of aldehyde to aliphatic amines being between 1.0:1 and 1.4: 1.

4. The grease composition of claim 3 in which the clay is a high base exchange clay selected from the group consisting of Wyoming bentonite and hectorite.

5. The grease composition of claim 3 in which the clay is hectorite.

6. The grease composition of claim 3 in which the lubricating base oil is a liquid organo-silicone polymer.

7. The grease composition of claim 6 in which the lubricating base oil is a phenyl methyl polysiloxane oil.

References Cited by the Examiner UNITED STATES PATENTS 2,829,100 4/ 1958 Armstrong et a1 252-28 2,890,171 6/1959 Armstrong et a1 25228 3,036,001 5/1962 Loefiier 252-28 DANIEL E. WYMAN, Primary Examiner. 

1. A GREASE COMPOSITION CONSISTING ESSENTIALLY OF A MAJOR AMOUNT OF A LUBRICATING BASE OIL GELLED TO GREASE CONSISTENCY WITH A COLLOIDALLY DISPERSED CLAY, SAID CLAY BEARING ON THE SURFACES THEREOF FROM 0.8 TO 0.5 PARTS BY WEIGHT, BASIS CLAY, OF A RESIN FORMED BY THE CO-CONDENSATION REACTION OF THE AMINES MELAMINE AND BEZOGUANAMINE WITH AN ALIPHATIC ALDEHYDE HAVING UP TO ABOUT 6 CARBON ATOMS, SAID RESIN HAVING BEEN FORMED IN THE PRESENCE OF A MINERAL ACID IN EXCESS OF THAT REQUIRED TO ACIDIFY THE SURFACES OF THE CLAY, THE MOLAR RATIO OF MELAMINE-TO-BENZOGUANAMINE BEING FROM 0.8:1 TO 5.0:1, AND THE EQUIVALENT RATIO OF ALDEHYDE TO ALIPHATIC AMINES BEING BETWEEN 0.9:1 AND 1.5:1. 